This invention relates to improvements in chain saw design and more particularly, to a novel chain saw structure comprising flexible and resilient skid and vibration isolating skid mountings which cooperate to:
1. reduce handle vibration, PA1 2. eliminate certain resonance, and PA1 3. reduce tendencies for the saw to creep while resting on the ground and idling.
It is well known that internal combustion engine powered chain saws tend to produce vibrations which may cause the operator of the chain saw to become somewhat fatigued. In response to this problem, vibration isolation systems have been provided which, in general, are interposed between the drive assembly of the chain saw and the handles so that vibration is reduced in the handle portions of the chain saw. Examples of such vibration isolation systems are disclosed in U.S. Pat. Nos. 3,813,766 (June 4, 1974), 3,652,074 (Mar. 28, 1972), 3,698,455 (Oct. 17, 1972) and 3,542,095 (Nov. 24, 1970), all to Frederickson et al. and U.S. Pat. No. 3,972,119 (Aug. 3, 1976) to Bailey.
In addition, chain saws typically have a flat surface on the bottom portion of the engine housing or other structure upon which the chain saw may be rested when not in use. If the engine is idling, vibrations may resonate through the flat surface and cause the saw to creep or "walk" to a different orientation or location.
In most chain saws of this type, the crank shaft of the engine is oriented transversly to the longitudinal, front-to-back, central axis of the saw. It is the motion of the piston, connecting rod, and crank shaft which produce vibrations which contribute to handle vibration and to "creeping" effect.
In order to reduce the magnitude of these problems and in order to achieve other significant advantages, the invention provides a novel skid and skid mounting for use with a chain saw.
A major advantage of the novel, flexible and resilient skid presented through the invention, and its integrally associated, stress relieving mounting means (affording torsional stress relief at the rear chain saw handle and axial stress relief at the front chain saw handle) entails a marked reduction in chain saw handle vibration and an elimination of certain resonance, with a consequent reduction in operator fatigue.
The skid comprises a structure which is preferably made of elastically flexible sheet material and which preferably spans the length of the chain saw drive assembly below the chain saw. The skid may have a flat portion upon which the saw may be rested, including a foot rest portion which the operator can utilize to anchor the saw while he starts the engine by pulling on a conventional starter cable. The skid is attached to a front handle, and both the skid and handle are linked to a drive assembly by a first attachment means which provides stress relieving action with respect to both the front handle and the skid. Preferably, the first attachment means includes means for providing axial stress relieving action longitudinally of the saw and resiliently cushioned radial relative movement between the drive assembly and the handle and the skid, with respect to the longitudinally extending, axial stress relieving axis.
The skid also comprises a rear portion which extends upwardly from the foot rest portion and is connected to a rear handle of the chain saw by a second attachment means which provides torsional stress relieving action between the rear handle and the skid. Preferably, the second attachment means also comprises a resilient member which provides resiliently cushioned radial and axial relative movement between the rear handle and the skid.
In a preferred embodiment of the invention, the skid is formed from a single sheet of resilient, preferably metallic, leaf spring-like material. Bumpers are interposed between the skid and the lower portion of the drive assembly, which bumpers, together with the resilient members forming the parts of the respective attachment means, provide vibration isolating skid support means and reduce resonant vibration.
The front attachment means preferably comprises a slide bar rigidly connected to the drive assembly and oriented substantially parallel to the chain saw's longitudinal axis. Resilient sliding means in the form of a rubber diaphragm is mounted for axial sliding movement on the slide bar and connected to the front handle and to the skid. The preferred construction for the second attachment means comprises a shaft connected to the rear handle of the saw and having a central axis which may be inclined with respect to the saw's longitudinal axis. A resilient annular member is mounted for axial rotation on the shaft and is connected to the upwardly extending rear portion of the skid. Furthermore, in the preferred flexible skid, the body of the springlike skid, due to its flexibility, provides a lowered spring rate and hence a lowered vibration and a reduction or elimination of resonant frequency vibration tendencies.
The rear portion of the skid and the foot rest together serve as a guard for the hand of the user and provide protection against accidental actuation of the trigger by an obstruction when the saw is set on the ground.
The novel structural concepts heretofore set forth are intended to produce, as primary objects of the invention, a chain saw structure characterized by a reduction or minimization of handle vibration and a reduction or minimization of resonant frequency vibrations in the chain saw.
An additional object of the invention is to provide a skid upon which a chain saw may be rested and which is substantially vibrationally isolated from the drive assembly of the saw such that vibration of the skid is prevented or inhibited.
Another object of the invention is to prevent vibrational creep of a chain saw, while the chain saw is resting on the ground.
Still another object is to provide structure on a chain saw which performs the multiple functions of acting as a guard for the trigger and hand of the user, acting as a foot rest for aid in starting the motor, and acting as a rest surface for placing the chain saw on the ground.